1. Field of the Invention
This invention relates generally to sheet accumulators and more particularly to an improved accumulator mechanism and an improved method for the accumulation into stacks of a number of seriatim-fed sheets, including different sizes, selectively in the manner of "over" or "under" accumulation.
2. Prior Art and Other Considerations
Various accumulators have been employed for the accumulation into stacks of sheet material such as paper sheets, documents, and the like. For instance, Luperti et al. disclose in U.S. Pat. No. 4,805,891 a standard and reverse collator for stacking sheets of paper fed in seriatim thereto from a singulating feeder in the same or reverse order as the sheets appear in the singulating feeder. Sheets are fed between moving, endless, elastic belts; ride over a stationary ramp guide; and, are thusly delivered over or under prior sheets that have been stopped against a registration device. Adjustment of the location of the ramp guide provides for delivery over or under prior sheets. The registration device is movable to release an accumulated stack of sheets for further transport after a desired number of sheets has been accumulated. Another example of an accumulator that relies on a similar ramp-guide mechanism is disclosed by Golicz in U.S. Pat. Nos. 4,799,663; 4,925,362; and 4,925,180.
Whereas prior art accumulators are in many ways satisfactory, high-speed handling imposes rather strict requirements upon reliability of operation and accuracy of registration of sheets in an accumulated stack. Moreover, interposition of stationary members, such as ramps, in the delivery path of sheets causes possibly undesirable, inadequately-controllable frictional effects between ramp surfaces and sheets that can result in misalignments. Accumulating mechanisms involving significant frictional effects between stationary members and the sheets have not been entirely satisfactory in high-volume and high-speed sheet processing particularly for accumulating different and mixed sheet sizes and sheets that are relatively short in the direction of transport. Further, the need for sheet handling equipment to reliably accumulate sheets into larger stacks imposes additional stringency on reliability and accuracy of operation. Hence, inadequately-controllable, varying frictional effects have been found to be undesirable.
The roller-accumulator of the present invention reduces and avoids difficulties and problems of the aforementioned kind by positively driving sheets to the stacking location without having to encounter stationary members along which undesirable frictional effects might arise.
Accordingly, an important overall feature of the invention is the provision of an improved accumulator and an improved method for the accumulation into stacks of a number of seriatim-fed sheets. The instant invention permits the selective inclusion of different sheet sizes, in the manner of "over" or "under" accumulation, wherein the accumulator mechanism drives sheets between moving belts so that they are positively nipped between moving rollers to a stacking location.